https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108356
Bug ID: 108356
Summary: Dead Code Elimination Regression at -O2 (trunk vs.
12.2.0)
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at ywg dot ch
Target Milestone: ---
Created attachment 54231
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54231&action=edit
presented code as file
cat case.c #93
char a;
static char c = 3;
char d;
void foo();
short(b)(short e, short f) { return e + f; }
int main() {
unsigned g = 0;
if (c)
;
else
foo();
for (; g < 2; g = b(g, 2)) {
d = g ? 0 : a;
if (g)
c = 0;
}
}
`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2` can not eliminate
`foo` but `gcc-releases/gcc-12.2.0 -O2` can.
`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB1:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
cmpb $0, c(%rip)
je .L6
.L4:
movzbl a(%rip), %eax
movb %al, d(%rip)
xorl %eax, %eax
addq $8, %rsp
.cfi_remember_state
.cfi_def_cfa_offset 8
ret
.L6:
.cfi_restore_state
xorl %eax, %eax
call foo
jmp .L4
---------- END OUTPUT ---------
`gcc-releases/gcc-12.2.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB1:
.cfi_startproc
movzbl a(%rip), %eax
movb %al, d(%rip)
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=6b156044c12bc4582511fe270b10450c943476dd
